Missing properties from base class when recursive types are involved.

[slobo-showbie]

When a type hierarchy as follows is constructed and the base class' type is constructed first by the TypeFactory then serializing the sub class fails due to missing properties from the base class.

class Base implements IFace<Sub> { @JsonProperty int base = 1 }
class Sub { @JsonProperty int sub = 2 }
interface IFace<T> {}

Serializes sub as {"sub":2} where {"base":1,"sub":2} is expected.

I've created a minimal scenario of this bug here: https://github.com/slobo-showbie/jackson-recursive-type-bug
I've experienced this bug in 2.7.8, 2.8.8, and 2.8.8.1

[slobo-showbie]

The reason the Base's fields are not serialized is that AnnotatedClass#_findFields does not return the fields from Base. Now, _findFields makes the assumption that if a class has no super class then it must be an Object or Interface (their fields are not to be returned). In order for _findFields to work the JavaType for Sub must be SimpleType and for Base also SimpleType. However in this case Sub is still a SimpleType but Base is a ResolvedRecursiveType; ResolvedRecursiveType does not return a super class, so Base's fields are ignored by _findFields.

The reason Base is a ResolvedRecursiveType is because of TypeFactory's cache. Consider:

1.   typeFactory.constructType(Base.class); // caches the type for Sub.class
2.   typeFactory.constructType(Sub.class); // returns from the cache

On line 1 constructType performs a recursive traversal like this:

Base(SimpleType) -> IFace<Sub>(?) -> Sub(SimpleType) -> Base(ResolvedRecursiveType)

The second time Base is reached a ResolvedRecursiveType is generated rather than a SimpleType. However, also the intermediate types are cached, so the cached result returned by line 2 is

Sub(SimpleType) with superclass = Base(ResolvedRecursiveType)

However if only line 2 is called without line 1, then the following would have been returned

Sub(SimpleType) with superclass = Base(SimpleType)

[cowtowncoder]

Excellent detective work!